Viewport options in Blender 2.90: where to configure Active outline and world grid?
It turns out that the correct place to change this is &quot;Viewport Overlays&quot; dialog. It's accessible via third dropdown in viewport top right with icon that looks like outline circle and filled circle partially overlapped. The tooltip for the quick toggle says &quot;Show overlays&quot;.
Other possible reasons for this behavior can be found at question Grid floor disappears and cannot see outline of selected objects